ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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heat and light causing its destruction. As a general rule, the maximum 
of acid corresponds to a minimum of aqueous vapour transpired, and 
vice versa. 
Tannin in the Compositae.* — According to M. L. Daniel the organ 
in the Compositae which contains the largest quantity of tannin is the 
leaf, next the capitulum, next the stem, and lastly, the root. The root 
is richest in tannin when young, while the reverse is the case with the 
stem and the leaves. Etiolation decreases the amount of tannin. The 
Cynaraceae contain, as a rule, a larger quantity of tannin than the 
Cichoriaceae. The above facts lead the author to the conclusion that, 
in the Compositae, the tannins cannot play the part of reserve-substance 
like inulin. 
Localization of the Essential Oil in the Tissue of the Onion. | — 
M. Voigt finds in various species of Allium that the essential oil of 
onion is found throughout the epiderm or the external layers of all 
parts of the plant, in the envelopes of the fruit and seed, in the layer 
of endosperm which surrounds the embryo, and in the sheaths of the 
vascular bundles. He believes its function to be to protect the plant in 
general against herbivorous animals, and especially the parts which 
conduct water and sap. 
Occurrence and Function of Phloroglucin.! — Herr T. Waage has 
detected the presence of this substance in about 135 species of plants. 
It is the symmetrical trioxybenzol, and occurs not only free, but forms 
also complex compounds, especially bodies of the nature of ethers, 
corresponding to the glucosides, such as phloroglucides (hesperetin, 
naringenin, phloretin, quercetin, rhamnetin, &c.), or phloroglucosides 
(aurantiin, glycyphyllin, hesperidin, phloridzin, rhamnin, rutin, &c.). 
Phloroglucin is found chiefly in the following parts of the axis, — 
the epiderm, phellogen, phelloderm, cortical parenchyme, sclerenchyme, 
medullary rays (in Angiosperms), cambium, pith, aerial and root-hairs, 
endoderm, pericambium, root-cap, underground stems and roots, but not, 
or only to a much smaller extent, in the cork, bast-fibres, sieve-tubes, 
cambiform vessels, and wood-vessels ; it was found also in the leaves, 
sepals, petals, stamens, and carpels. The proportion of phloroglucin 
varies greatly in different plants ; as a general rule it is most abundant 
in Vascular Cryptogams, Gymnosperms, and dialypetalous Dicotyledons ; 
least so in Monocotyledons and sympetalous Dicotyledons. 
Phloroglucin C 6 H 6 0 3 may be formed, like the carbo-hydrates, by 
the mutual decomposition of carbon dioxide and water, with elimination 
of oxygen. It was never detected in the chlorophyll-grains or in the 
protoplasm of mature cells ; only in the cell-sap. It is probably formed 
as the result of a splitting-up of sugar into phloroglucin and water. It 
appears not to be used up again to any extent in the vital processes of 
the plant, but to be a secondary product of metastasis. 
* Rev. Gen. de Bot. (Bonnier), ii. (1890) pp. 391-403. 
t Jahrb. Hamburgischer Wiss. Anlage, 1890. See Bonnier’s Rev. Ge'n. de Bot., 
ii. (1890) p. 365. 
X Ber. Deutsch. Bot. Gesell., viii. (1890) pp. 250-92. 
1891. 
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